Composition/structure/property relations of multi-ion-beam reactive sputtered lead lanthanum titanate thin films: Part I
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This paper, the third and final of a three part series, presents the electrical properties of postdeposition annealed, lead lanthanum titanate (PUT) thin films deposited by multi-ion-beam reactive sputtering (MIBERS). Also, a model is presented that explains the relations among composition, crystallographic structure, microstructure, and electrical properties of the PLT thin films. Thin films of PLT consisting of the perovskite phase exhibit (100) textured microstructures. Addition of a critical quantity of excess PbO results in the loss of this (100) texture, and continuity of the perovskite phase is disrupted while both excess PbO and porosity phases become continuous due to a percolation effect. Films with textured microstructures consisting of a continuous perovskite phase exhibit relatively high dc resistivities, high dielectric permittivities, and high remanent polarizations. At the transition between textured and nontextured microstructures, a discontinuous drop in the electrical properties occurs due to the ensuing continuity of the excess PbO and porosity. These composition-induced changes in the electrical properties were quantitatively modeled by applying a simple mixing rule model to the microstructure model developed in Part II of this series.
I. INTRODUCTION The electrical properties of ferroelectric materials are governed by the composition-controlled crystal structure and microstructure. Fundamentally, composition determines both the potential to form a particular phase (perovskite for ferroelectric PLT) and the number of phases formed.1 Crystal structure defines the magnitude of the switchable polarization of a ferroelectric through acentric atom displacements.2 Microstructure demarcates the polar domains and crystalline (and amorphous) segments comprising the entire material.3'4 The relationships among composition, crystallographic structure, and microstructure of PLT thin films were presented in Parts I5 and II6 of this series of papers. This paper presents the electrical properties of postdeposition annealed, MIBERS-deposited, perovskite PLT thin films and also introduces a model that relates the electrical properties to the observed composition, crystallographic structure, and microstructure. The PLT system was chosen for study because a broad range of ferroelectric-based properties are obtained for the compositions over which the perovskite solid solution exists. Many different devices, such as ^Present address: Ecole Polytechnique Federale de Lausanne, Laboratoire de Ceramique, MX-D Ecublens, CH-1015, Lausanne, Switzerland. b *Also with Department of Engineering Science and Mechanics. J. Mater. Res., Vol. 8, No. 9, Sep 1993
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nonvolatile memories,7 dynamic random access memories (DRAM),8 piezoelectric surface acoustic wave (SAW) devices,9 pyroelectric sensors,10 and electrooptic modulators11 may be produced from PLT materials due to the wide range of properties. The ferroelectricbased properties of PLT are strongly dependent on the La an
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